Question

Which of the following is made of layers of ash and cooled lava flows? A. shield volcano C. composite volcano B. plateau basalts D. cinder cone volcano

Short answer

The answer is C: composite volcano.

Step-by-step solution

Understand the Options

Read and understand the different types of volcanic formations listed in the options: Shield volcanoes, composite volcanoes, plateau basalts, and cinder cone volcanoes.

Identify the Composition

Determine which of these formations is known for being made of layers. Shield volcanoes are characterized by gentle broad slopes formed by fluid lava. Composite volcanoes, or stratovolcanoes, are made up of alternating layers of lava flows, ash, and volcanic rocks. Plateau basalts form large, flat regions due to extensive lava flows. Cinder cone volcanoes are composed of pyroclastic fragments ejected from a single vent.

Compare with the Question Criteria

The question specifically asks for a formation made of layers of ash and cooled lava flows. From the understanding of compositions, composite volcanoes fit this description as they consist of alternating layers of lava and ash.

Confirm the Answer

Verify by cross-checking with basic volcanic geology knowledge. Composite volcanoes are indeed known for their stratified layers of hardened lava flows and volcanic ash.

Key concepts

Volcanic Formations

Volcanic formations are fascinating natural structures that come in various shapes and sizes. Each type of volcanic formation has unique characteristics that are dictated by the nature of volcanic eruptions and the type of materials ejected. Some common volcanic formations include:

• Shield Volcanoes: These have broad, gently sloping sides created by low-viscosity lava that can travel great distances.
• Composite Volcanoes: Also known as stratovolcanoes, these iconic cone-shaped mountains are formed from a mix of lava flows, volcanic ash, and rock fragments. Their layered structure results from alternating eruptions that vary in intensity and material.
• Plateau Basalts: These form when lava flows extend over large areas to form flat, wide regions. They result from massive eruptions that produce low-viscosity lava.
• Cinder Cone Volcanoes: These are the simplest type of volcano, comprised mainly of volcanic debris and pyroclastic fragments ejected from a single vent. They have steep, conical slopes.

Composite volcanoes are particularly interesting due to their complex structure and explosive eruptions, making them a focus of volcanic studies.

Lava Flows

Lava flows are streams of molten rock that pour or ooze from a volcanic vent during an eruption. The properties of these lava flows can vary greatly depending on factors like temperature, composition, and gas content. Understanding lava flows is important for grasping how different volcanic formations develop. There are two primary types of lava:

• Pāhoehoe Lava: This type is smooth and billowy, resembling coiled ropes when it cools. It flows slowly, allowing it to cover wide areas.
• 'A'ā Lava: Characterized by rough and jagged clumps, this type flows more quickly and forms steeper platforms as it cools.

Composite volcanoes often feature thick, viscous lava that cools and hardens slowly, contributing to their steep profiles. The alternating layers of such lava flows and volcanic ash build up the impressive mountainous structures seen in stratovolcanoes.

Volcanic Ash Layers

Volcanic ash consists of tiny fragments of rock, minerals, and volcanic glass created during explosive eruptions. When a volcano erupts, ash is ejected into the atmosphere and can travel long distances before settling on the ground. Understanding volcanic ash layers is crucial for piecing together the eruption history of a volcano. These layers provide evidence of past eruptions, detailing their timing and impact. In composite volcanoes, ash layers play a significant role:

• These layers alternate with lava flows, contributing to the stratified appearance of the volcano.
• Ash deposits can solidify into tuff, a porous rock that adds to the formation's overall structure.
• Over time, these repeated deposits create a record of past volcanic activity, aiding in understanding the behavior of the volcano.

The intricate blend of ash and solidified lava layers in composite volcanoes makes them both beautiful and hazardous – potentially impacting vast areas if they erupt explosively.